The present invention relates to a high-speed copying apparatus which is capable of producing a plurality of copies of an original by subjecting the original to exposure scanning only once.
Several methods of producing a plurality of copies of an original using only one electrostatic latent image have been proposed for a copying apparatus of this general type. According to one of the conventional methods, a single electrostatic latent image is repeatedly used to produce a plurality of copies. However, the method is disadvantageous in that, as the number of copies increases, the quality of the reproduced images is degraded. That is, the quality of each reproduced image is lower than that of the preceding image because the surface potential of the photosensitive body gradually decreases with an increasing number of copies after the latent image has been formed. In another method, two photosensitive drums are employed to eliminate the above-described difficulty. Since it is difficult to produce a number of copies at high speed using a method wherein an original is scanned linearly and repeatedly, the image of the original is formed as a toner image on the surface of the first photosensitive drum and the toner image is used as a secondary original. As the secondary original can be scanned by turning the first photosensitive drum, the copying speed can be increased. The image of the secondary original is formed on the second photosensitive drum and is then transferred onto a recording sheet.
An example of a high-speed copying apparatus operating according to this conventional method is shown in FIG. 1. Referring to FIG. 1, as a first stage of the process, an original 1 to be copied is illuminated by an illuminating device 2. Light from the original thus illuminated (optical data) is reflected by a mirror 3, passed through a projecting lens 4, reflected by a mirror 5 and a movable mirror 6-1, and then applied to the surface of a first photosensitive drum 7a thus forming the image of the original on the surface of the first photosensitive drum 7a. As the first photosensitive drum 7a has been previously charged by a charging unit 13a, the electrostatic latent image is formed as a result of the formation of the original image. The latent image thus formed is developed into a toner image by a developing device 14a. The image of the original 1 is formed as a visible toner image on the surface of the first photosensitive drum 7a to provide a secondary original image. In a second stage of the process, the secondary original image is illuminated by an illuminating device 10 disposed near the first photosensitive drum 7a. Light from the secondary original image thus illuminated (optical data) is reflected by the aforementioned movable mirror 6-1 whose reflecting surface has been turned counterclockwise through about 90.degree. from its position in the first stage of the process. The light thus reflected passes through a second projecting lens 4b, reflected by a mirror 9, and applied to the surface of a second photosensitive drum 7b which has been charged by a second charging device 13b thus projecting the secondary original image onto the surface of the second photosensitive drum 7b. This image is developed by a developing device 14b, transferred onto a recording sheet delivered from a copying sheet supplying device 16 by a transferring device 15, and fixed by a fixing device 17.
The implementation of this method requires two photosensitive drums, namely, the first and second photosensitive drums 7a and 7b, two processing devices such as the discharging devices 11a and 11b, the charging devices 13a and 13b, the developing devices 14a and 14b and cleaning devices 12a and 12b, and two projecting lenses 4a and 4b. In addition, there is a requirement for a mechanism for controlling the synchronous operation of the two photosensitive drums. Accordingly, a copying apparatus operating in accordance with this method is considerably expensive due to component and manufacturing costs. In order to project the image formed on the first photosensitive drum 7a onto the second photosensitive drum 7b using the second projecting lens 4b, some space must be provided therebetween which results in a large overall size of the copying apparatus.
Accordingly, an object of the present invention is to eliminate all the drawbacks accompanying a conventional copying apparatus. More specifically, an object of the invention is to provide a copying apparatus which uses only one photosensitive drum to provide a number of copies of high image quality in a short period of time, and which has a low manufacturing cost and small size.